Circuit arrangement for generating saw-tooth oscillations



P 1952' J; J. P. VALETON 2,61

CIRCUIT ARRANGEMENT FOR GENERATING SAW-TOOTH OSCILLATIONS FiledAug. 2

JOSU E JEAN PHIL IPPE VALETON AGENT l atented Sept. 16, 1952 emcurr ARRANGEMENT FOEGENERAT'iNd Y SAW-TOOTH OSCILLATIONS ilos'u le an Philippe 'ValetonnEimihoven,.Nethere g.

' lands, assignor to Hartford-NationalBankiand. Trust Company, LHartford; Comm :as-Etrus-tee Appueauoniiu usta 1948,seria1 No;41;928

li'ifflieNetherlands August 15,1947

1 This invention relates to a circ'uit arrangement for producing sawtooth oscillations and comprising a condenser which is periodically charged by way or an impedance and subsequently discharged by way of the series-connection of a rectifier and a winding of a transformer having a term-magnetic core, thecondenser voltage being supplied'to theoontrol grid of a discharge tubewhich' tube is controlled by synchronisation signals and the output circuit of which comprisesanother transformer winding which is inductively coupled with the firstmentioned windinginsuch'manneras to cut off the rectifier during the'charging operation of the condenser.

Such a known circuit arrangement is shown in Fig. 1. p

The control-grid" circuitwf a discharge tube I comprises a condenserfwhich'is charged by means of a battery 3' and'a resistance 4. I The series-arrangement of an inductance 5 and a rectifier 6 is connected'inparallelwiththe-condenser 2. The 'induct'ance'i constitutes oneof the-windings of the transformer "which-hash ferromagnetic core '8 and of which theseeond winding 9 is interposedin'theano'de circuit of "the discharge tube l, whichtube'is supplied 'witlrcurrent from the anode*voltage'batt'ery l0.

synchronisation signals aresuppliedto thegrid of tube I.

For the sake of 'cleariiess" the operation of this known circuit-arrangement will be' briefly'--explained, with the use of"-a"'voltage at the fcon denser 2 of a polarity 'asindicated"inthedraw- If this voltage is 'such'z'that the tube! is cut off so that no current appears in the-outputcirwit and consequently no voltage is set up 'across the inductance 5, the condenser is charged; from the battery 3 by way-of the resistanc'e' l; Charging continues even on attaining'a voltage-at'which the tube 1 is made. conducting sinc'eflue to'the anode current then appearingaconstantwoltage of the "polarity is setup across the inductance-'5, as a result of which the rectifier'6 is cutoff;

As soon, however, as'theincrease"infanode current falls off,fwhich"mayibe caused by the supply of a pulse-to one'of'th'egrids ofthetube 5 of suitable polarity, a voltageof opposite'sign is set up across the inductance 5. If this voltageexceeds the voltage at theicondenser- 2, the rectifier 6 passes current. In'this event-the total magnetic energypresent inthe'induetance -'I discharges through the rectifier 6 and 'the condenser charge resumes its initial state; Owing to unilateral'vconductionrlthez rectifierifi: this proce s is tenninate'dnasrsoon as thezourrentriinthem rfl cuit -i'changes its :polarit-y :which 1 occurs; after; a quarterJcycleof thezperiodxof. oscillation :detere mined-bylthe jcapacity :ofrthe:condenserand, the inductanoeofcoihE: :l, Y

The cycle describedar'is repeated .so; that..-:thc voltageattheieondenserexhibits azsawtdothzwave form, and :the current: appearing ;in1.;the:;output CirGuitrOL-tUbGIL isasawtoothmurrentze :7 p

With the .use of synchronisationzsignals: such a circuit-arrangement exhibits therldisadvanta fi that the amplitude o-ithe; sawtooothitvoltageran thasawtoothmurrentismot constant .1 V ,7

' J Thisfdisadvantageemay:begavoidedgin:a,'kndwn mannen-by: means :of; the. ;rectifier. H and the source of direct voltage- .12 shownin .dotted lines in Figl-i. As soonrasi theiamplitudeof the saw:- tooth voltage at the condenser.:.-2 exceeds-the maximum value. determinedmy: the voltageuof the battery l 2, the rectifier'. I Lbecomes conduct-.- ing, so that :a satisfactory limitation is obtained. Alternatively, theparallel-connection of a condenser and -a resistance-"havinga high time cons'tant maybe substituted forthe; battery l2.

However, such a limitationcircuit-exhibits several disadvantages; iFir'st-ofalranadditionalrectifier "and: an 'addi-tional'battery-or -RC circuit are required. I Moreover, "the --additiona;l -comp1ication arises that the sawtoothwoltageis set up-atthe cathode of thedio'de', Due to this either an:additional winding one the. supply "transformer will berequired for heating thefiilamentof the diode, or a diode. of V particularconstruction should; be provided which iscapable of withstanding acorn: paratively high alternating voltage betweenfjthe heating element and .the electron-emitting 1 part oftheeathode; Y M

The circuit,-arrangernent-according to the in,- vention, which; has also for sits object to" keep constant the am i ud o the se iqq hv tionymeets thesedraW-backs and exhibits the tea-- 1 ture r that the size 10f. the itransformer -:-is such that the. transformer .o i m netism intothe area of saturation-:durmg' the ,last part cyof- -the sweep of the sawtoothzc rrlentzin;th aoutput circuitof the, discharge tube. 1

Such a magnetisationresultsin thatntne induc- I ,tance v.L of "the -.windin'g; 9 considerably decreases by the end orthe; sweep'ro the; s t e haeu re Owing .to this. the magnetic energyrfo liiidi accumulated in the zinductancertr which ,is g,-r e sponsible for the maXimum'eVOItageisetrupgatgthecem denser '2, .wil-lbnly slightly increase;- ins'spite'Q a 3 further increase of the current i in the inductance.

The variation of the inductance L of coil 9 as a function of the current strength 1' through the winding is shown in Fig. 2 in which furthermore the time t is plotted downwards on the vertical axis.

If the time t and consequently the current 1' increase, the inductance L will decrease so that the magnetic energy Li is substantially limited.

In a suitable form of the circuit-arrangement according to the invention such a limitation may be obtained in a very simple manner if the transformer core consists of a ferromagnetic, homogeneous or substantially homogeneous, cubic, simple or composite ferrite.

Such a ferrite may be represented by the formula MFezO4, which may also be conceived-as MOFezOa and in which M is a bivalent metal or a combination of two bivalent metals accordin as to whether a simple or a compositeferrite is concerned. It is to benoted that the composition need not strictly satisfy the expression MO.Fe2Os, but that the relative quantities MO and F6203 may vary within such limits as to avoid separation of a second crystal phase by which the magnetic properties are adversely affected.

By means of a core of such material an inductance variation of the winding 9 as a function of the current strength according to Fig. 2 is easily ensured.

In this respect it is pointed out that with the use of the aforesaid ferrites as core material, the transformer may be given a very suitable size also in connection with the further conditions imposed i. e. the obtainment of a sufiiciently high voltage across the winding Sand maximum avoidance of magnetic losses.

In fact, a judicious choice of bivalent metals and a suitable method of manufacture of the material permit ferrites to be obtained of which the initial permeability exceeds 60, and the tan or the loss angle 6, measured witlra closed annular core and extrapolated to a field strength zero, may be smaller than 0.06.

Although, in the circuit-arrangement according to the invention, limitation of the amplitude of the sawtooth voltage at the condenser 2 is fundamentally not as exact as the limitation ensured by means of the diode and the source of direct voltage shown in dotted lines in Fig. 1, the circuit according to the invention, when used for producing the deflection currents of cathodebeam tubes, for instance in television reception, proves to satisfy the most stringent conditions imposed.

This is even so if the deflection coils are coupled by way of a transformer to the output circuit of the tube I, and the grid circuit of this tube comprises a network by which any deviations from the linear course of the sawtooth current, which are caused by the interposition of the last-mentioned transformer, are corrected.

Such a circuit-arrangement is shown in Fig, 3 in which the parts corresponding to Fig. I bear the same reference numerals.

The deflection coils i3 of the cathode-beam tube are coupled, by way of a transformer i4, with the output circuit of the discharge tube I. As the frequency of the sawtooth voltage is lower and the inductance of the primary winding [5 smaller, the deviation from linearity of the sawtooth current will be greater in the coils I3.

In order to correct this distortion, the grid circuit comprises a phasing network is by means of which the voltage set up across the condenser 2 is distorted in such manner as to re-establish the linearity of the current in the coils [3.

It has been found that in such a circuit the amplitude variation of the sawtooth current across the condenser 2 is much greater than in the circuit represented in full lines in Fig. 1.

In the circuit shown in Fig. 3, also, a limitation satisfying all conditions imposed is obtained if during the last part the sweep of the sawtooth current in the output circuit of the discharge tube, the core of the transformer l is magnetised .into the area of saturation so that this circuit also need not comprise any additional circuit elements.

What I claim is:

1. A sawtooth generator for a cathode-ray tube having deflection coils, said generator comprising an electron discharge tube having a cathode, a grid and an anode, a condenser connected in the cathode-grid path of said tube, an impedance, a voltage source connected in series with said impedance across said condenser in a polarity increasing the conductivity of said tube in the course of charging, a first transformer having a primary coil and a secondary coil and ferro magnetic core, a rectifier connected across said condenser in series with said secondary coil, a second transformer having a primary winding and a secondary winding, said secondary winding being adapted for connection to said deflection coils, an output circuit including means connecting said primary coil and said primary wind ing in the anode-cathode path of said tube in a direction at which the resultant voltage induced in said secondary coil maintains said rectifier non-conductive in the course of said charging, means to apply synchronizing pulses to said tube to decrease the conductivity thereof and thereby render said rectifier periodically conductive, whereby a sawtooth current fiows in said output circuit, a phase-shifting network interposed between said condenser and said cathode-grid path to effect a phase displacement substantially equal and opposite to that caused by said second transformer, said first transformer having a characteristic at which during the last part of the sweep insaid sawtooth current said core is magnetized to within the area ofsaturation.

2. A sawtooth generator comprising an electron discharge tube having a cathode, a control electrode and an anode, a condenser connected in the cathode-control electrode path of said tube,

'- means to apply a charging potential across said condenser in a polarity increasing the conductivity of said tube in the course of charging, a transformer having a primary and a secondary and a ferro-magnetic core, a discharge circuit for said condenser including a unidirectional device connected in series with said secondary across said condenser, an output circuit including means connecting said primary in the anodecathode path of said tube in a direction at which the resultant voltage induced in said secondary maintains said uni-directional device non-conductivefduring the charging of said condenser, and means to apply synchronizing pulses to said tube to decrease .the conductivity thereof and thereby render said uni-directional device periodically conductive, whereby a sawtooth current flows in said output circuit, said transformer having a characteristic by which during the last part of the sweep in said sawtooth current said core is magnetized to within the area of saturation, said term-magnetic transformer core being constituted by a substantially homogeneous, cubic, simple ferrite.

3. A sawtooth generator comprising an electron discharge tube having a cathode, a control electrode and an anode, a condenser connected in the cathode-control electrode path of said tube, means to apply a, charging potential across said condenser in a polarity increasing the conductivity of said tube in the course of charging, a'

transformer having a primary and a secondary and a ferro-magnetic core, a, discharge circuit for said condenser including a uni-directional device connected in series with said secondary across said condenser, an output circuit including means connecting said primary in the anodecathode path of said tube in a, direction at which the resultant voltage induced in said secondary maintains said uni-directional device non-conductive during the charging of said condenser, and means to apply synchronizing pulses to said tube to decrease the conductivity thereof and thereby render said uni-directional device periodically conductive, whereby a sawtooth current flows in said output circuit, said transformer 6 having a characteristic by which during the last part of the sweep in said sawtooth current said Y core is magnetized to within the area of saturation, said ferro-magnetic core being constituted by a substantially homogeneous, cubic, composite ferrite.

JOSUE JEAN PHILIPPE VALETON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

